ENTHALPY-ENTROPY COMPENSATION PHENOMENA IN WATER SOLUTIONS OF PROTEINS AND SMALL MOLECULES - A UBIQUITOUS PROPERTY OF WATER
ENTHALPY-ENTROPY COMPENSATION PHENOMENA IN WATER SOLUTIONS OF PROTEINS AND SMALL MOLECULES - A UBIQUITOUS PROPERTY OF WATER
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DOI：
10.1002/bip.1970.360091002
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发表时间：
1970-01-01
期刊：
影响因子：
2.9
通讯作者：
RAJENDER, S
中科院分区：
文献类型：
--
作者：
LUMRY, R;RAJENDER, S
本文证明了小分子溶质在水溶液中各种过程的熵变与焓变之间存在着特定的线性关系。这些过程包括离子和非电解质的溶剂化、水解、氧化还原、弱电解质的电离以及吲哚荧光的猝灭等。对于所有这些过程，比例常数的值（称为补偿温度）都在一个相对较窄的范围内，从250 ° K到315 °K。这种行为可能是实验误差的结果，但对于许多过程，数据的精度足以表明熵-熵补偿模式是真实的。它是暂时得出的结论是，该模式是真实的，非常常见的，无论溶质和溶质过程研究的液体水作为溶剂的性质的后果。因此，这种现象要求通过包括对负责补偿行为的水的特性的特定处理来扩展对水中溶质过程的理论处理。该效应的可能基础被认为是与温度无关的热容量变化和/或两种现象上显着的水物质浓度的变化。这些替代品的光谱和弛豫研究所建议的水的两态过程的关系进行检查。在各种蛋白质反应中，焓变和熵变之间存在类似且可能相同的关系，这表明液态水在许多蛋白质过程中起着直接作用，并且可能是蛋白质生理功能的共同参与者。建议将线性熵-熵关系用作水参与蛋白质过程的诊断测试。在此基础上，胰凝乳蛋白酶和乙酰胆碱酯酶的催化过程受本体水的性质支配。血红蛋白与氧的结合也属于同一类。研究小溶质和蛋白质过程行为的相似性和差异，以显示它们如何相关。没有肯定的结论成立，但它是可能的，蛋白质的过程耦合到水通过膨胀和收缩的蛋白质和一般的特殊模式的熵-熵补偿是一个后果的性质，水的性质，需要膨胀和收缩的溶质的影响附近的液体水的自由体积的变化。它表明，蛋白质可以预期，以响应附近的水和界面自由能的膨胀和收缩的变化。这种反应可以解释蛋白质溶液的各种目前无法解释的特性。更一般地说，熵-熵补偿模式似乎是“结构形成”和“结构破坏”的热力学表现，这两个操作上定义的术语在水溶液的讨论中经常使用。如果是这样的话，补偿模式是普遍存在的，需要重新检查大量的分子解释来自定量研究的过程中的水。为了适应水行为的这一方面，可能必须扩展水中过程的理论。
This article presents evidence for the existence of a specific linear relationship between the entropy change and the enthalpy change in a variety of processes of small solutes in water solution. The processes include solvation of ions and nonelectrolytes, hydrolysis, oxidation–reduction, ionization of weak electrolytes, and quenching of indole fluorescence among others. The values of the proportionality constant, called the compensation temperature, lie in a relatively narrow range, from about 250 to 315 °K, for all these processes. Such behavior can be a consequence of experimental errors but for a number of the processes the precision of the data is sufficient to show that the enthalpy–entropy compensation pattern is real. It is tentatively concluded that the pattern is real, very common and a consequence of the properties of liquid water as a solvent regardless of the solutes and the solute processes studied. As such the phenomenon requires that theoretical treatments of solute processes in water be expanded by inclusion of a specific treatment of the characteristic of water responsible for compensation behavior. The possible bases of the effect are proposed to be temperature‐independent heat‐capacity changes and/or shifts in concentrations of the two phenomenologically significant species of water. The relationship of these alternatives to the two‐state process of water suggested by spectroscopic and relaxation studies is examined. The existence of a similar and probably identical relationship between enthalpy and entropy change in a variety of protein reactions suggests that liquid water plays a direct role in many protein processes and may be a common participant in the physiological function of proteins. It is proposed that the linear enthalpy–entropy relationship be used as a diagnostic test for the participation of water in protein processes. On this basis the catalytic processes of chymotrypsin and acetylcholinesterase are dominated by the properties of bulk water. The binding of oxygen by hemoglobin may fall in the same category. Similarities and differences in the behavior of small‐solute and protein processes are examined to show how they may be related. No positive conclusions are established, but it is possible that protein processes are coupled to water via expansions and contractions of the protein and that in general the special pattern of enthalpy–entropy compensation is a consequent of the properties of water which require that expansions and contractions of solutes effect changes in the free volume of the nearby liquid water. It is shown that proteins can be expected to respond to changes in nearby water and interfacial free energy by expansions and contractions. Such responses may explain a variety of currently unexplained characteristics of protein solutions. More generally, the enthalpy–entropy compensation pattern appears to be the thermodynamic manifestation of “structure making” and “structure breaking,” operationally defined terms much used in discussions of water solutions. If so, the compensation pattern is ubiquitous and requires re‐examination of a large body of molecular interpretations derived from quantitative studies of processes in water. Theories of processes in water may have to be expanded to accommodate this aspect of water behavior.